In the Linux kernel, the following vulnerability has been resolved:

mlxsw: spectrum_buffers: Fix memory corruptions on Spectrum-4 systems

The following two shared buffer operations make use of the Shared Buffer Status Register (SBSR):

devlink sb occupancy snapshot pci/0000:01:00.0

devlink sb occupancy clearmax pci/0000:01:00.0

The register has two masks of 256 bits to denote on which ingress / egress ports the register should operate on. Spectrum-4 has more than 256 ports, so the register was extended by cited commit with a new port_page field.

However, when filling the registers payload, the driver specifies the ports as absolute numbers and not relative to the first port of the port page, resulting in memory corruptions [1].

Fix by specifying the ports relative to the first port of the port page.

[1] BUG: KASAN: slab-use-after-free in mlxsw_sp_sb_occ_snapshot+0xb6d/0xbc0 Read of size 1 at addr ffff8881068cb00f by task devlink/1566 […] Call Trace: dump_stack_lvl+0xc6/0x120 print_report+0xce/0x670 kasan_report+0xd7/0x110 mlxsw_sp_sb_occ_snapshot+0xb6d/0xbc0 mlxsw_devlink_sb_occ_snapshot+0x75/0xb0 devlink_nl_sb_occ_snapshot_doit+0x1f9/0x2a0 genl_family_rcv_msg_doit+0x20c/0x300 genl_rcv_msg+0x567/0x800 netlink_rcv_skb+0x170/0x450 genl_rcv+0x2d/0x40 netlink_unicast+0x547/0x830 netlink_sendmsg+0x8d4/0xdb0 __sys_sendto+0x49b/0x510 __x64_sys_sendto+0xe5/0x1c0 do_syscall_64+0xc1/0x1d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f […] Allocated by task 1: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0x8f/0xa0 copy_verifier_state+0xbc2/0xfb0 do_check_common+0x2c51/0xc7e0 bpf_check+0x5107/0x9960 bpf_prog_load+0xf0e/0x2690 __sys_bpf+0x1a61/0x49d0 __x64_sys_bpf+0x7d/0xc0 do_syscall_64+0xc1/0x1d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 1: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 kasan_save_free_info+0x3b/0x60 poison_slab_object+0x109/0x170 __kasan_slab_free+0x14/0x30 kfree+0xca/0x2b0 free_verifier_state+0xce/0x270 do_check_common+0x4828/0xc7e0 bpf_check+0x5107/0x9960 bpf_prog_load+0xf0e/0x2690 __sys_bpf+0x1a61/0x49d0 __x64_sys_bpf+0x7d/0xc0 do_syscall_64+0xc1/0x1d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/942901e0fc74ad4b7992ef7ca9336e68d5fd6d36
• https://git.kernel.org/stable/c/bf8781ede7bd9a37c0fcabca78976e61300b5a1a
• https://git.kernel.org/stable/c/bfa86a96912faa0b6142a918db88cc0c738a769e
• https://git.kernel.org/stable/c/c28947de2bed40217cf256c5d0d16880054fcf13